1. Technical Field
This application relates to chemical analysis and more particularly to systems and methods that use the nuclear quadrupole resonance effect to detect certain types of materials.
2. Background
Systems that use the Nuclear Quadrupole Resonance (NQR) effect to detect the existence of certain materials are known in the art. One example system was described in U.S. Pat. No. 8,660,803 assigned to AMI Research and Development, LLC, the assignee of this application, hereby incorporated by reference. These systems use one or more conductive surfaces to define a space or portal that is to be monitored. Two or more wire loops are disposed within the space typically adjacent the conductive surfaces. The wire loops are each individually electrically terminated in one arrangement; alternatively, they can be arranged as balanced transmission lines. The wire loops are driven with a radio frequency (RF) transmitter to create time varying electromagnetic fields of various types within the defined space.
The time varying electromagnetic fields stimulate Nuclear Quadrupole Resonance (NQR) in any material with an electric quadrupole moment, thereby causing the material(s) to emit coherent RF emissions. By utilizing Rabi transitions the nucleus of material atoms oscillates between a first and second state, under the time dependent incident electromagnetic field, and alternately absorbs energy from the incident field while emitting coherent energy via stimulated emission. These stimulated emissions are then received. The received RF emissions are then further processed to determine characteristics of the substance, such as by detecting the amplitude, phase and/or frequency, and comparing them to the responses for known materials.